1. Field of Invention
The invention relates to a linear illuminator using a light guide member.
2. Description of Related Art
An illuminator for linearly irradiating light flux emitted from a point light source, such as an LED or the like, is used as an illuminator for reading an image in, for example, a facsimile machine or a copying machine using an electrophotographic system. Such an illuminator has an advantage that light can be irradiated to an original with high efficiency and the illumination intensity to the original can be enhanced with low power consumption.
However, if the number of LEDs is reduced to attain the low power consumption, the illumination intensity to surface areas on the original which face, or oppose, the LED chips is high, however, the illumination intensity to surface areas on the original opposing the spaces between the LED chips is low, resulting in a non-uniform illumination intensity (illuminance) distribution.
Therefore, in order to solve the problem of the non-uniform illuminance distribution in the linear illuminator using the point light source, such as an LED or the like, as described above, there has been proposed a linear illuminator using a light guide member 62 which comprises a rectangular-parallelepiped light guide unit 60 of a light translucent member and a cylindrical lens unit 61 which is formed of a light translucent member so as to be continuous with the light guide unit 60 as shown in FIG. 10.
In the linear illuminator using the guide light member 62 as described above, an LED 63 serving as a point light surface is fixed to an end face in the short length direction of the light guide unit 60, and a diffusion reflection unit 64, for reflecting or diffusing light flux to a face of the light guide unit 60, is positioned opposite to a light-flux emission face comprising the cylindrical lens unit 61 and reflects the light through the body of the light guide unit 60.
According to the linear illuminator described above, light flux can be irradiated onto the original with high efficiency, the illumination intensity to the original can be enhanced with low power consumption and a substantially uniform illuminance distribution can be obtained.
However, according to the above conventional linear illuminator, the light flux emitting portion is formed of a cylindrical lens. The light flux is diffused and reflected by the diffusion and reflection unit 64 of the light guide member 62. Therefore, the light flux emitted from the light-flux emission face of the cylindrical lens suffers spherical aberration on the original P. Accordingly, the light flux near to the optical axis is focused to a position farther from the original P while the light flux far from the optical axis is focused to a position before the face of the original and thus the light flux is irradiated onto the original in the form of a wide band. Therefore, the illumination intensity (illuminance) on the original P is lowered.
In order to compensate for the above problem, the illumination intensity required for a reading operation is secured by using a high-brightness LED, and the reading time is lengthened to keep the reading quality, so that the price of the illuminator itself is increased and the reading speed is lowered.
The invention has been implemented in view of the foregoing problems, and has an object to provide a linear illuminator which can irradiate light onto an original with high efficiency, keep sufficient illumination intensity (illuminance) to the original with low power consumption and obtain a uniform illumination intensity distribution.
In order to attain the above object, according to a first aspect of the invention, a linear illuminator for linearly irradiating light flux from a light source onto the surface of an original by a pillar-shaped light guide member formed of a light translucent member is characterized in that the light source is secured to the end face of the light guide member which corresponds to the bottom surface of the pillar body, and the light guide member comprises a focusing lens unit having a light flux emitting face at the position corresponding to the side surface of the pillar shape, a light guide which is continuously formed at the focusing lens unit, and a diffusion and reflection unit provided at the confronting side to the light flux emitting face through the light guide unit, wherein the light flux emitting face of the focusing lens unit serves as a non-cylindrical face to set the diffusion and reflection unit and the surface of the original in a conjugate positional relationship with each other.
According to the linear illuminator of the first aspect of the invention, when the light flux is emitted from the light source secured to the end face at the position corresponding to the bottom surface of the pillar body of the end surfaces of the pillar-shaped light guide member formed of the translucent member, the light flux propagates through the light guide unit of the light guide member while it is repetitively totally reflected from the inner surface of the light guide unit of the light guide member. The light flux which is incident to the diffusion and reflection unit provided at the confronting side to the light flux emission face through the light guide unit through the repetitive total reflection is diffused/reflected at the diffusion and reflection unit, and emitted from the light flux emission face which is the outer surface of the focusing lens unit formed continuously with the light guide unit and formed at the position corresponding to the side surface of the pillar body. In this case, the light flux emission face of the focusing lens unit is a non-cylindrical face, and it is designed so as to set the diffusion and reflection unit and the surface of the original in a conjugate positional relationship with each other. That is, it is not formed by a conventional general design method in which the light source is set as an object point and the surface of the original is set as an image point, but it is formed by a novel design method in which the diffusion and reflection unit is considered as a secondary light source and the non-cylindrical face design of the light flux emission face is promoted by setting the diffusion and reflection unit and the surface of the original as an object point and an image point respectively.
The light flux emission face of the invention is a non-cylindrical face to set the diffusion reflection unit and the surface of the original in the conjugate position relationship with each other. Therefore, the light flux emitted from the diffusion and reflection unit suffers no spherical aberration and is focused in an extremely narrow linear form on the surface of the original. Therefore, the focusing efficiency is high, and outstanding illumination can be performed with light flux having a uniform illuminance distribution.
According to a second aspect of the invention, in the linear illuminator of the first aspect of the invention, the locus of the light flux emission face on a section parallel to the end face of the light guide member is expressed by the following equation:
n(y2+(l0xe2x88x92z)2)xc2xd+(y2+(l1+z)2)xc2xd=nl0+l1,
where l0 represents the length on the z-axis from the face top to the diffusion and reflection unit, l1 represents the length on the z-axis from the face top to the surface of the original and n represents the refractive index of the light guide member to air in a coordinate system in which the surface top of the light flux emission face is set to the origin of the coordinate system, the optical axis is set to the z-axis and the axis vertical to the optical axis is set to the y-axis.
According to the linear illuminator of the second aspect of the invention, the locus of the light flux emission face on a section parallel to the end face of the light guide member of the linear illuminator is expressed by the following equation:
n(y2+(l0xe2x88x92z)2)xc2xd+(y2+(l1+z)2)xc2xd=nl0+l1,
where, in a coordinate system in which the surface top of the light flux emission face is set to the origin of the coordinate system, the optical axis is set to the z-axis and the axis vertical to the optical axis is set to the y-axis, l0 represents the length on the z-axis from the face top to the diffusion and reflection unit, l1 represents the length on the z-axis from the face top to the surface of the original and n represents the refractive index of the light guide member to air. Accordingly, in a case where the diffusion and reflection unit is regarded as a secondary light source, setting the diffusion and reflection unit as an object point and setting the surface of the original as an image point, an object point on the optical axis, that is, each point in the diffusion and reflection point is focused onto one point in the image point, that is, one point on the surface of the original. As a result, the light flux emitted from the diffusion and reflection unit is focused on the surface of the original in an extremely narrow linear shape. Therefore, the focusing efficiency is enhanced and outstanding illumination can be performed with light flux having a uniform illuminance distribution.
According to a linear illuminator of a third aspect of the invention, in the linear illuminator of the first aspect of the invention, the original illumination width bxe2x80x2 of the original on the surface of the original is expressed by the following equation:
bxe2x80x2=xe2x88x92axcex2/cos xcex8,
wherein on the section parallel to the end face of the light guide member, a represents the width of the diffusion and reflection unit in the direction vertical to the optical axis, xcex2 represents the lateral magnification of the focusing lens unit and xcex8 represents the angle of the surface of the original to the direction perpendicular to the optical axis.
According to the linear illuminator of the third aspect of the invention, the original illumination width bxe2x80x2 of the original on the surface of the original is expressed by the following equation:
bxe2x80x2=xe2x88x92axcex2/cos xcex8,
wherein on the section parallel to the end face of the light guide member of the linear illuminator according to the first aspect of the invention, a represents the width of the diffusion and reflection unit in the direction vertical to the optical axis, xcex2 represents the lateral magnification of the focusing lens unit and xcex8 represents the angle of the surface of the original to the direction perpendicular to the optical axis.